1. Field of Use
This invention relates generally to multisection telescopic crane boom having a rotatable screw for extending and retracting boom sections and, in particular, to movable support means for the screw.
2. Description of the Prior Art
U.S. Pat. No. 3,836,011 discloses a telescopic or extensible crane boom of a type wherein two boom sections are moved relative to each other by means of an elongated hydraulic cylinder unit disposed within the boom. In that extensible boom, a buckling-preventing support for the hydraulic cylinder unit is employed in the boom wherein an intermediate position of an optionally extendible piston-rod of the cylinder unit is always supported with a buckling-preventing support having legs slideably or rotatably engaged with inner circumference of a boom member. That patent further discloses driving means for the buckling-preventing device which moves the device to said intermediate position of the piston-rod in connection with the operation of the cylinder unit.
In some telescopic booms, however, wherein an elongated rotatable screw is employed instead of a hydraulic cylinder unit to extend and retract the boom sections, it is also sometimes necessary to provide support means for the screw but insofar as applicant is aware no such support means are known or available.